Drillers and oil field operators use electromagnetic logging tools to measure a wide variety of subsurface formation parameters including, e.g., resistivity and nuclear magnetic resonance (NMR) responses. Such tools often energize a transmitter antenna with an alternating current to emit electromagnetic energy through the borehole fluid and into the surrounding formations. The emitted energy interacts with the borehole and formation to produce signals that are detected and measured by one or more receiver antennas. By processing the detected signal data, a profile of the formation can be determined. Such information is useful for well exploration and production.
The antennas on these tools are generally formed as multi-loop coils of conductive wire. The conductive wire sustains a voltage drop when the transmitters are driven and the signals are induced into the receivers. Depending on the winding pattern for the coils, such voltage drops can create an unwanted dipole signal that adversely affects the measurements. In addition, such voltage drops can cause undesirable cross-coupling between the antennas, further contaminating the tool's measurements. These issues do not appear to have been adequately addressed in tools having transverse (X- and Y-) antennas.